Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Annotations already declare readOnlyHint, idempotentHint, and openWorldHint=false, so the safety profile is covered. The description adds genuinely new behavior: the exact fields returned and the empty-account interpretation ('user is brand new'), which no structured field provides. Returns format is described, though pagination/limits are not mentioned.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Is the description appropriately sized, front-loaded, and free of redundancy?

Four short sentences that are front-loaded with the purpose, followed by return shape, empty-state handling, and prerequisite note. Each sentence carries information, though the return-field enumeration makes it slightly list-heavy for a tool whose schema already has no parameters.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

For a no-parameter, no-output-schema list tool, the description supplies the return fields, the empty-account meaning, the downstream routing to create_brand, and its prerequisite role. There is no output schema to lean on, and nothing an agent needs to call it correctly is missing.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

The tool takes zero parameters, so there is no parameter semantics to document and the baseline is 4 by rule. The description appropriately spends its budget on return fields and workflow placement instead.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Does the description clearly state what the tool does and how it differs from similar tools?

States a specific verb+resource and defines the domain term ('brands (businesses / clients)') so an agent knows exactly what is listed. It distinguishes from create_brand and list_ad_accounts by clarifying the resource is the brand/client entity, not the ad account.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Does the description explain when to use this tool, when not to, or what alternatives exist?

Explicitly positions the tool as the 'Required first step for most other tools' and routes the empty-result case to create_brand with a coaching instruction. Both the when-to-use and the alternative path are named, leaving nothing to inference.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.